1. Field of the Invention
The invention generally relates to cataract and glaucoma surgical methods, and to sensors for measuring the intraocular pressure of an eye. More particularly, the invention relates to a corneal intraocular pressure sensor and a surgical method that utilizes the corneal intraocular pressure sensor.
2. Background
Corneal scarring is a major cause of blindness, especially in developing countries. There are various causes for corneal scarring, which include: bacterial infections, viral infections, fungal infections, parasitic infections, genetic corneal problems, Fuch's dystrophy, and other corneal dystrophies. A corneal transplant is often required if the corneal scarring is extensive, and cannot be corrected by other means. However, there can be major complications associated with a corneal transplant, such as corneal graft rejection wherein the transplanted cornea is rejected by the patient's immune system.
A normal emmetropic eye includes a cornea, a lens and a retina. The cornea and lens of a normal eye cooperatively focus light entering the eye from a far point, i.e., infinity, onto the retina. However, an eye can have a disorder known as ametropia, which is the inability of the lens and cornea to focus the far point correctly on the retina. Typical types of ametropia are myopia, hypermetropia or hyperopia, and astigmatism.
A myopic eye has either an axial length that is longer than that of a normal emmetropic eye, or a cornea or lens having a refractive power stronger than that of the cornea and lens of an emmetropic eye. This stronger refractive power causes the far point to be projected in front of the retina.
Conversely, a hypermetropic or hyperopic eye has an axial length shorter than that of a normal emmetropic eye, or a lens or cornea having a refractive power less than that of a lens and cornea of an emmetropic eye. This lesser refractive power causes the far point to be focused behind the retina.
An eye suffering from astigmatism has a defect in the lens or shape of the cornea converting an image of the point of light to a line. Therefore, an astigmatic eye is incapable of sharply focusing images on the retina.
While laser surgical techniques, such as laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) are known for correcting refractive errors of the eye, these laser surgical techniques have complications, such as post-operative pain and dry eye. Also, these laser surgical techniques cannot be safely used on patients with corneas having certain biomechanical properties. For example, corneal ectasia may occur if these laser surgical techniques are applied to patients having thin corneas (e.g., corneas with thicknesses that are less than 500 microns).
Therefore, what is needed is a method for corneal transplantation that reduces the likelihood that the implanted cornea will be rejected by the patient. Moreover, a method is needed for corneal transplantation that is capable of preserving the clarity of the transplanted cornea. Furthermore, there is a need for a method of corneal transplantation that reduces the likelihood that the transplanted cornea will be invaded by migrating cells. Also, what is needed is a method for corneal lenslet implantation for modifying the cornea to better correct ametropic conditions. In addition, a method is needed for corneal lenslet implantation that prevents a lens implant from moving around inside the cornea once implanted so that the lens implant remains centered about the visual axis of the eye.
Moreover, many cataract patients experience complications following their cataract surgery. For example, opacification of the lens capsule affects about 80-90% of the eyes after cataract surgery because of proliferation of the remaining cells in the lens capsule. This post-surgery opacification requires a laser disruption of the posterior capsule for the patient to see.
Also, conventional monofocal intraocular lenses do not permit accommodation. As such, patients with monofocal intraocular lenses typically require reading glasses after cataract surgery.
Therefore, it is apparent that a need also exists for treatment of cell proliferation of the lens capsule after cataract extraction, and for an accommodative intraocular lens implant that enables the cataract patient to see both far and near objects without the need for supplemental lenses, such as reading glasses.
Furthermore, cataract patients who additionally have glaucoma pose difficult challenges for the treating ophthalmologist. When glaucoma is associated with a cataract in the same patient, the two surgeries must often be performed at the same time. However, unfortunately, both conditions can have their own complications. For example, as mentioned above, opacification of the lens capsule affects about 80-90% of the eyes after cataract surgery because of proliferation of the remaining cells in the lens capsule. This post-surgery opacification requires a laser disruption of the posterior capsule for the patient to see. Similarly, after glaucoma surgery, the connecting hole from the eye to the subconjunctival space may become plugged by fibrous proliferation occurring after surgery in an attempt to reject the shunt after the surgery or even a shunt in place, as a response of the surgical procedure creating a hole in the eye wall to drain the intraocular fluid.
Therefore, it is apparent that a need further exists for treatment of cell proliferation of the lens capsule after cataract extraction, and for treatment of fibrous cell proliferation after glaucoma surgery with or without a drainage tube.
Glaucoma is a disease that affects the eye and is considered one of the major causes of blindness in the world. There are many forms of glaucoma, having different pathogenesis. Among these are open angle glaucoma (OAG) where the anterior chamber located between the cornea and the iris is open, closed angle glaucoma where the anterior chamber angle is closed, and secondary glaucoma caused by different etiologies, but often an inflammatory process proceeds its occurrence. The glaucoma can be congenital or acquired, and some have genetic predisposition. Regardless of its pathogenesis, the hallmark of the disease is mostly an increased intraocular pressure (IOP), except for in the low tension glaucoma where the IOP appears to be normal, but the patient has the other symptoms of glaucoma. The other characteristic findings in glaucoma eyes are the cupping of the optic nerve head, and the loss of the nerve fiber layer of the retina and ganglion cells of the retina. These can lead to, or can also be considered a consequence of a degenerative process affecting potentially the retinal ganglion cells and an imbalance of the IOP and intracranial pressure leading to gradual loss of the visual field that can be constricted with time or completely lost resulting in blindness.
There are many treatment modalities in managing the disease processes. Since the IOP is, in most cases, elevated beyond a normal level of 10-20 mmHg, routine checking of the IOP including potentially a 24-hour or more measuring of these values during the day and night is needed to find out if there are any pressure variations during the course of the day, especially during sleep where the IOP generally is raised. These pressure variations can obviously compromise the retinal nerves and circulation, even if the pressure is within a normal range of 10-20 mmHg, such as in patients with low tension glaucoma. Thus far, the measurement of the IOP has been sporadic because it is limited by a patient's visit to the doctor's office.
The treatment for glaucoma has been mostly medicinal, that is by applying antiglaucoma medication(s) as eye drops to reduce the intraocular pressure. If the IOP cannot be controlled, either by laser surgery of the angle or ciliary body processes where the fluid is produced, then alternatively, one tries to drain the intraocular fluid to outside of the eye through a stent or shunt opening with one end in the anterior chamber and the other end located in the subconjunctival space or connecting the intraocular fluid via a shunt tube from the inside the eye to the choroidal space. In some situations, the surgeon makes a small hole in the eye wall connecting the anterior chamber fluid or aqueous directly to the subconjunctival space. There are a number of variations of this surgery having the same goal of reducing the IOP to a normal level. The glaucoma can also be associated with a cataract and not seldom requires doing the two surgeries at the same time. However, unfortunately both conditions can have their own complications (e.g., opacification of the lens capsule after cataract surgery affecting about 80-90% percent of the eyes because of proliferation of the remaining cells in the lens capsule, and requiring a laser disruption of the posterior capsule for the patient to see). Similarly, after glaucoma surgery, the connecting hole from the eye to the subconjunctival space can become plugged by fibrous proliferation occurring after surgery with or without a shunt tubing.
Recently, efforts have been made experimentally to measure the intraocular pressure via a contact lens positioned on the surface of the cornea for a duration of 24 hours with a pressure sensor and transmit the information wirelessly to a receiver mounted on an eye glass frame. The disadvantage of this contact lens system is that the system provides the measurement of the IOP indirectly from the eye cavity and depends on how the corneal curvature is deformed in response to the IOP. Also, the contact lens can be worn only for a short time because, otherwise it can interfere with the corneal oxygenation that happens mostly from the outside air and nutrition of the cornea that is, in part, supplied by the tear film that is compromised by placement of a static contact lens on the cornea. The chances of a corneal abrasion is increased by the described shortcomings, and for the patient, the placement and removal of the contact lens is particularly difficult in elderly patients.
Another recent effort has implanted such a system inside the lens capsule of the eye, by removing the natural crystalline lens, but leaving the lens capsule intact so that the device can be positioned inside the lens capsule and measure the IOP, and then transmit it outside the eye to a receiver. Because the system disposed in the lens capsule requires a battery to operate, the eventual need to replace the battery necessitates another surgical procedure to be performed later. Also, the initial surgical procedure has its own serious complications, and often is not justified when one is dealing with young patients or children. In addition, this process creates capsular opacification, it deprives the patient from the use of his or her natural lens, and can have the lifelong potential complication of inflammation that aggravates the existing glaucoma itself.
Therefore, it is apparent that a need further exists for an intraocular pressure measurement device and a method using the same that eliminates the shortcomings of the aforedescribed procedures.